The invention relates to a multifunctional refrigerant container that is suitable in particular for use in a cooling system designed for operation with a two-phase refrigerant to cool food on board an aircraft. The invention further relates to a method of operating such a refrigerant container.
A cooling system that is suitable for operation with a two-phase refrigerant is known from DE 10 2006 005 035 B3 and is used for example to cool food that is stored on board a passenger aircraft and intended for issuing to the passengers. Typically the food provided for supplying to the passengers is kept in mobile transport containers. These transport containers are filled and precooled outside of the aircraft and after loading into the aircraft are deposited at suitable locations in the aircraft passenger cabin, for example in the galleys. In order to guarantee that the food remains fresh up to the time of being issued to the passengers, in the region of the transport container locations cooling stations are provided, which are supplied with cooling energy from a central frigorific device and deliver this cooling energy to the transport containers, in which the food is stored. In this case, compared to frigorific units formed separately at the individual transport container locations a cooling system with a central frigorific device offers the advantage of a smaller installation volume and reduced weight and moreover entails less outlay for assembly and maintenance. What is more, given the use of a cooling system with a central frigorific device disposed outside of the passenger cabin it is possible to avoid machinery noise that is generated by frigorific units positioned in the region of the transport container locations and is audible in the aircraft passenger cabin and hence may be found intrusive.
In the cooling system known from DE 10 2006 005 035 B3 the phase transitions of the refrigerant flowing through the cooling circuit that occur during operation of the system enable the latent heat consumption that then arises to be utilized for cooling purposes. The refrigerant mass flow needed to deliver a desired cooling capacity is therefore markedly lower than for example in a liquid cooling system, in which a one-phase liquid refrigerant is used. Consequently, the cooling system described in DE 10 2006 005 035 B3 may have smaller line cross-sections than a liquid cooling system with a comparable cooling capacity. The reduction of the refrigerant mass flow moreover makes it possible to decrease the delivery rate needed to feed the refrigerant through the cooling circuit of the cooling system. This leads to an increased efficiency of the system because less energy is needed to operate a corresponding feed device, such as for example a pump, and moreover less additional heat, which is generated by the feed device during operation of the feed device, has to be removed from the cooling system.
A problem associated with the cooling system disclosed in DE 10 2006 005 035 B3 is however the high rest pressure of the refrigerant that may arise in the idle state of the system if in the idle state of the system the refrigerant is in the gaseous state of aggregation. Whereas the rest pressure of the refrigerant in a liquid cooling system that uses for example Galden® as a refrigerant is usually at most ca. 20 bar, in a cooling system designed for two-phase operation that uses for example CO2 as a refrigerant pressures of 170 to 220 bar may arise at a system temperature of ca. 85° C. The line system of the cooling system is consequently subject to considerable mechanical stress and has to be designed accordingly.
DE 10 2009 011 797 A1 therefore proposes equipping a cooling system described in DE 10 2006 005 035 B3 with a control valve, which is disposed in the cooling circuit of the cooling system and which, upon transfer of cooling system to its idle state, is controlled in such a way that a desired operating pressure arises in the cooling circuit downstream of the control valve. Refrigerant cooled by the frigorific device is received in a reservoir disposed upstream of the control valve in the cooling circuit.
By means of the operating method described in DE 10 2009 011 797 A1 it is possible effectively to prevent a region of the cooling circuit situated upstream of the control valve, i.e. the lines and other components, such as for example valves, heat exchangers etc., that are provided in this region of the cooling circuit, from being acted upon in the idle state of the cooling system by the high maximum rest pressure of the two-phase refrigerant that arises if the refrigerant is in the gaseous state of aggregation. Instead, the region of the cooling circuit situated downstream of the control valve may be held under a comparatively low operating pressure.
With the cooling systems of prior art there is the problem that it is often difficult to accommodate the system components in the only very limited amount of installation space available on board an aircraft or even to position these in such a way relative to one another that for example by utilizing the force of gravity during process control an optimally efficient operation of the cooling system is made possible.